Electric resistor and its process of manufacture



Patented Jan. 15, 1924.

JOHN F. DIBZU'WEIT,

OF LAUREL, MARYLAND, ASSIGNOR ONE-HALF TO WILLIA w. VA'BNEY, OF BALTIMORE, MARYLAND.

ELECTRIC RESISTOR AND ITS PROCESS OF MANUFACTURE Application filed November 11, 1920. Scrlal No. 423,282.

1'0 all whom it may concern:

Be it known that I, JOHN F. Dmznwnrr, a citizen of the United States, residing at Laurel, in the county of Prince Georges and State of Maryland, have invented a certain. new and useful Improvement in Electric Resistors and Their Process of Manufacture, of which the following is a specification, reference being had to the accompanying drawings, forming a part hereof.

My invention relates to electric resistors and especially to the method of their construction and treatment.

It has been the custom heretofore to con struct resistors of irregular pieces of broken carbon or graphite, 01' to use continuous rods of carbon or.other material. Resistors are also constructed of regularly-shaped blocks or discs, which by reason of their high contact resistance, lend themselves especially well for the construction of amechan-ically strong element.

One of the chief disadvantages of all ofthe above named resistor elements is their rapid disintegration at even moderate temperatures when in contact with oxygen. To obviate this especially in their use inthe electric furnace, attempts have been made to prevent disintegration by operating such resistors in an atmosphere of producer gas, by introducing such as into the melting chamber. This metho while exercising a beneficial action is impractical, as it is necessary to open the furnace frequently for charging and pouring and if the internal pressure of the furnace is below atmospheric pressure, air will enter the furnace and will form an explosive mixture causing serious accidents to life and property.

Attempts have also been made to protect resistors against the detrimental effects of the contained oxygen by surrounding them with a layer of silicon earbide,but such resistors are not practical for metallurgical electric furnaces, where close temperature regulations are required.

It is known in. the art that when a carbon filament is heated to incandescence' in a hy Ciro-carbon atmosphere, that any irregu larities in the shape of the filament are automatically-equalized, as at temperature above 3000 degrees F. the hydro-car on gas breaks down and the free carbon combines with the hottest part of the filament where the temperature is the highest.'

It is also known in the art that carbon or any carbonaceous material when in contact with silica: will absorb the silica, and at cer:

tain high temperatures form silicon-carbide.

This silicon-carbide is not easily attacked by oxygen, and if the penetration of the silica has reached sufiicient depth, carbon may be made immune to oxygen provided the temperature does not reach the volatilization.

resents in a longitudinal section part of a.

heating furnace provided with one or more of my resistor elements; Fig. 2, shows an end elevation of my resistor element; Figs.

'3 and 4 show side and end elevations of electric furnaces comprising. several such resistor elements.

Similar numerals refer to similar parts throughout the several views.

1- and 2' are solid carbon or graphite electrodes which serve as current conductors to blocks or discs 3 composed of carbonaceous material. The number of these-discs may be varied to suit different potentials. The electrodes 1 and 2 terminate inmetallic electrode holders 8 and 9 and which are water cooled by water chambers 26.' a

Surrounding the complete electrode or resistor is a high refractory tube 5 tenninating also in the metallic electrode holders 8 and 9. This tube may be made of any suitable material such as alundum, or silicon carbide.

The space between the refractory tube 5 and the carbon resistor is filled with pure silica sand 3 and is tightly packed. Electrodes 1 and 2 are fitted with metallic screw caps 6 and 7 slidably located in recesses to allow hand wheels 12 and 13 to exert pressure upon discs 3 to increase or decrease the resistance of the contact surfaces. Yokes 10 and 11 are supports for hand screws 12 and 13. Pipe 14 provides means for introducing any kind of inert or reducing gas into i the space filled with silica sand and pipe the above gas (say illuminating gas) is alwhen a temperature of 34.00 degrees F. is

till

lowed to flow through the space filled with silica sand surrounding the resistor elementuntil all of the oxygen is expelled.

From the above it will be seen that by the operation of the furnace at high temperatures my improved resistors are made in place. I prevent the oxygen of the atmosphere from combining with the carbon by impregnating or case hardening the carbon or graphite electrode with silica or silicic acid. The process of doing the above is as follows:

The electrodes to be treated are packed with pure silica preferably of a size to pass Each through a number 20 mesh screen. I

The

electrode must be thoroughly covered.

ends of the electrodes are connected to current carrying electrodes of low potential. By passing electric current through the electrodes and resistors, heat is generated and reached the silica surrounding each electrode or resistor is decomposed and is absorbed by the carbon or graphite electrodes or resistors. The penetration of the silica into the surface of'the electrodes isa matter of time and can be controlled accordingly.

The properties acquired by the electrodes or resistors through the absorption of silica are very remarkable and make this material very desirable for the use of heating eiements for electric furnaces. From practical experience it has been found that these electrodes or resistors will stand up to temperatures of 3400 degrees F. Without any protection and can be exposed at that temperature to the atmospheric oxygen without eing affected.

This process will-also increase the mechanical strengthv of the electrodes thereby reducing losses through breakage.

All kinds of shapes of electrodesmay be treated and made by this process and I do not limit myself to any shape.

After the furnace'has been Working for some time in actual use, to properly case harden my resistors, the casing 5 and the surrounding silica may be destroyed or retering into combination with said resisting material. p

flxThe process of forming resistors consisting of aplurality of carbon sections aggregated, heating the aggregation to a sufii" cient temperature to cause the same 'to combine with silica supplied in a proper atmosphere in proximity thereto.

3. The process of forming resistors consi'sting of a plurality of carbon sections aggregated, heating the aggregation to a sutiicient temperature to cause the same to combine with silica supplied in a proper atmosphere in proximity thereto consisting of a hydrocarbon gas.

4. A. resistor comprising a resisting ma terial consisting of carbon blocks piled together, silica surrounding said pile and means of passing a gas through said silica.

5. A resistor comprising a. resisting material consisting of carbon blocks piled together, silica surrounding said blocks means of passing a gas through said silica, terminals to said resistor provided with means of cooling and means of conducting said gas.

6. A resistor comprising a resisting material consisting of carbon blocks piled to gether, silica surrounding said pile and means of passing a gas through said silica and means of compressing said resisting material.

7. An electric resistor provided with water I Witnesses: Brennan P. HUTCHINS, WILLIAM W. Vnunnr.

JOHN F. ninznwnrr. 

